Miniature electrodes for electrically sensing physical characteristics of electrolyte fluids are particularly useful for testing small fluid samples contained in small cells or beakers. A miniature electrode is defined in the industry as having an outside diameter of less than 12 millimeters, which is slightly less than one-half inch.
The conventional miniature electrode in the prior art has been formed from a hollow glass tube support with a glassy carbon disc fused over the lower end. A copper wire extends from the fused glassy carbon disc through the hollow glass tube to provide the electrical conductivity for the miniature probe. The glassy carbon disc and copper wire do not provide highly accurate current readings and thus the predictability and accuracy of the test results may be suspect. The glassy carbon electrode cannot be satisfactorily replaced by a more accurate noble metal electrode disc since a fluid tight seal with the glass tube is difficult, if not impossible, to obtain. Without a satisfactory seal, the highly corrosive electrolyte is free to seep into the glass tube and corrode the copper conductor to minimize or destroy the effectiveness of the miniature probe. Moreover, glass miniature probes are extremely fragile due to their glass construction and their small diameter relative to length. Therefore, the miniature glass electrodes are frequently broken requiring relatively expensive replacement.
The assignee of the present invention has sold a plastic electrode in several sizes, one of which approaches the outer diameter size of a miniature electrode. This plastic electrode included an electrode disc core comprising a noble metal electrode disc soldered to a stainless steel substrate. The substrate includes a smaller diameter disc projection and a larger diameter body section. The substrate body section had a threaded blind end bore adapted threadedly to receive part of the electrode arbor. The substrate and electrode disc were inserted into a TFE fluorocarbon sleeve having an outer diameter as small as 0.472 inches. The TFE fluorocarbon sleeve was shrunk fit into an interference fit with the stainless steel substrate to form a seal therebetween. While this electrode has successfully been used for several years, the TFE fluorocarbon sleeve may have oxygen bubbles captured therein or thereon which potentially might affect current readings when the TFE fluorocarbon sleeve is partially submerged in the electrolytic fluid.